GLB GELF

GLB GELF is a Go library used for structured log messages generation. They could be a directly stdout output type and/or an output to a Graylog server.

Installation

go get gopkg.in/Graylog2/go-gelf.v2/gelf
go get github.com/globocom/glbgelf

Usage

A previous initialization is required calling InitLogger(graylogAddr, appName, tags, dev) function.

• graylogAddr: Graylog address and port server. Format: string(hostname:port).
• appName: Application name that is using GlbGelf. Format: string(application_name).
• tags: Reference tags used for the app. This is a field used in the Graylog server. Format string(tag1, tag2, tag3, ...).
• development: Boolean defining the operation mode. Case it's true, logs will be send directly to stdout. Otherwise, it will send both stdout and Graylog server. Format boolean(true or false).

Through the inicialization function, struct Logger can be used in the application. This struct stores a list of parameters (listed bellow) previously defined and it has a function called SendLog for log message generation in Graylog format.

{
    "version": GLB GELF library version, 
    "host": Hostname, 
    "short_message": Message defined and generated in the app, 
    "full_message": Same message configured in the previous parameter, 
    "timestamp": Unix format timestamp message generation, 
    "level": Message loglevel, 
    "file": Correspodent file where the log message was generated, 
    "line": Log message line number, 
    "tags": Tags defined in the inicialization function, 
    "app": App's name defined in the inicialization function, 
    "extras": Extra field passed in a map[string]interface variable
    
}

function SendLog(extra map[string]interface{}, loglevel string, messages ...interface{})

where:

• extra: map struct with its string key defining the extra field name and interface value its content.

• loglevel: string defining message loglevel. Through the string, JSON "level" field is filled out with the correspondent numerical value. It is accepted the following strings (with its correspondent value). It is accepted the following loglevel strings:

  • "EMERG": loglevel 0.
  • "ALERT": loglevel 1.
  • "CRIT": loglevel 2.
  • "ERROR": loglevel 3.
  • "WARNING": loglevel 4.
  • "NOTICE": loglevel 5.
  • "INFO": loglevel 6.
  • "DEBUG": loglevel 7.

• messages: string that fills "short_message" and "full_message" fields.

Usage examples

The example bellow shows previous defined functions being called and the message log output expected.

import "github.com/globocom/glbgelf"

glbgelf.InitLogger("log.example.com:12201","app-name","TAG1,TAG2,app-name",true)

glbgelf.Logger.SendLog(nil, "INFO", "First gelf message! :)")

Log message output expected:

{
    "version":"1.1",
    "host":"xyz.local",
    "short_message":"First gelf message! :)",
    "full_message":"First gelf message! :)",
    "timestamp":1515535933,
    "level":6,
    "app":"app-name",
    "file":"/go/src/testing_logger.go",
    "line":19,
    "tags":"TAG1,TAG2,app-name"
}

Usage example defining new extra fields in the log message. Map variable is defined with the extra fields and its contents.

glbgelf.Logger.SendLog(map[string]interface{}{"result":"error","action":"status","info":"DB", "time":1.0, "rid":"A03B3755-0ABC-44B2-97DF-4BDCAAFDCC9F"}, "ERROR", "Database verification failed!")

The following log message output contains the extra fields defined in the map variable.

{
    "version":"1.1",
    "host":"xyz.local",
    "short_message":"Database verification failed!",
    "full_message":"Database verification failed!",
    "timestamp":1515602054,
    "level":3,
    "action":"status",
    "app":"app-name",
    "file":"/go/src/testing_logger.go",
    "info":"DB",
    "line":19,
    "result":"error",
    "rid":"A03B3755-0ABC-44B2-97DF-4BDCAAFDCC9F",
    "tags":"TAG1,TAG2,app-name",
    "time":1
}

Environment Variables

• GELF_GRAYLOG_SERVER: Environment variable with graylog server address and port. If Graylog server is initialized with an empty string in InitLogger function, the value stored in this ENV will be used;

• GELF_APP_NAME: ENV used to store app's name. It will be used in case where an empty string is passed to InitLogger function.

• GELF_TAGS: It will store tags in case an empty tag string is passed in InitLogger function.